1. Field of the Invention
The invention relates to a power supply device and, more particularly, to a current regulator with two power supplies.
2. Description of the Related Art
Generally, peripherals are powered via universal serial bus (USB) interfaces or the power over Ethernet (POE) technology.
According to the standard, the USB interface can provide the maximum power 2.5 W, and the general POE can provide the maximum power 15 W. If the wattage consumed by the product is larger than the maximum wattage provided, a “bottleneck” will appear in product design. To provide the product with larger input wattage, design engineers usually connect two USB interfaces or two POEs in parallel and reduce voltage difference between the two power supplies to avoid supplying power by a single power supply. However, the method cannot ensure the current of the two input sources in balance.
According to current limitation stipulated in the USB and POE, the USB interface can only provide a current of 0.5 A, and the POE mode of Ethernet can provide a voltage of 48V and the maximum current of 0.35 A. However, a problem will occur when load is provided for a user side by combining the two voltages. So long as one voltage is a little higher than the other one, the higher voltage will provide current for the user side. Therefore the lower voltage will not output current for the load. A general motherboard provides the maximum current of 0.5 A for the USB interface. When the current is larger than 0.5 A, a compulsive protection for the motherboard will be carried out to keep the motherboard and back end safe. Apparently, it may be limited in application when the current is not balanceable. For example, the input power supply stops providing power. Many “bottlenecks” occur because the current is not balanceable. Therefore more breakthroughs are expected, and this is just the issue that the invention overcomes.